In order to produce high quality images, there is a need for correcting images in systems where the integration period (exposure time) is not defined in the imager, because external stimulus can introduce errors between the desired exposure time and the true integration period. This is particularly applied to intensity correction in Time Delay Integration (TDI) imaging systems.
In some TDI systems, there is a significant variation of image intensity during a TDI scan. This effect is strongly correlated to changes in the stage velocity. Since snapshot TDI converts a desired exposure time to a stage velocity, corresponding trigger count, and corresponding encoder counts per trigger, certain physical effects (i.e., variation in stage velocity, friction, propagation delay, clock jitter, etc.) can impact the actual exposure time. The principal cause for such variation of image intensity is the result of a model calculation being applied to a real world system.
The method for correcting intensity once the true exposure is known is common knowledge to those in the field. Succinctly, since illumination is constant, the accumulation of intensity in a focal plane array increases linearly with time. Therefore, multiplying the acquired intensity by the ratio of desired exposure time to realized exposure time on a frame by frame basis corrects the difference in intensity proportionally.
However, the method for acquiring the exposure time, particularly in the case of TDI is hardly studied. Applying an exposure correction to a Snapshot TDI has never been done before. Traditional approaches to TDI use an essentially continuous exposure and have no definition of a discrete frame (i.e., traditional TDI results in many lines of data that form a continuous image). However, Snapshot TDI consists of several discrete exposure periods, thereby allowing for a definition of exposure time since there are discrete frames. Therefore, there is a need for a method for correcting for correcting images acquired via an asynchronously triggered acquisition, such as a TDI scan.